Breast cancer is the most common type of cancer and the second leading cause of cancer death among women with more than one million new cases and 370,000 deaths worldwide yearly. Chemotherapy drugs, such as Doxorubicin, have been used in both pre- and post-operative adjuvant therapy or as the main therapeutic option for breast cancer patients with metastatic disease. Although recent advances in the combination of chemotherapy drugs have improved survival for breast cancer patients, a high percentage of patients develop resistance to chemotherapeutic agents and fail treatment. Therefore, novel approaches for the effective treatment of breast cancer are urgently needed to improve the therapeutic response. This project aims to develop a Doxorubicin loaded and target specific magnetic iron oxide nanoparticle (IONP) platform for targeted therapy of breast cancer. The proposed nanodrug can be systemically delivered and selectively accumulated at the primary and metastatic tumor sites and subsequently internalized into breast cancer cells via endocytosis. Selective enrichment of the IONP in tumor cells and the tumor environment produces strong MRI contrast for the detection of drug delivery and response in the tumor lesions by MR imaging. After demonstration of the feasibility that the engineered nanodrug can target the tumor in an animal model, the goal of this SBIR Phase II project is to extend the investigation of the successes in the Phase I study and move closer to translating this platform into preclinical trials and commercialization by further optimizing the targeted theranostic nanodrug platform for efficacy, biodistribution, toxicity, pharmacokinetics/pharmacodynamic studies, and future clinical trials.